A number of motionless mixer types exist, such as Multiflux, helical and others. These mixer types, for the most part, implement the same general principle to mix fluids together. In these mixers, fluids are mixed together by dividing and recombining the fluids in an overlapping manner. This action is achieved by forcing the fluid over a series of baffles of alternating geometry. Such division and recombination causes the layers of the fluids being mixed to thin and eventually diffuse past one another. This mixing process has proven to be very effective, especially with high viscosity fluids. Static mixers are typically constructed of a series of alternating baffles, of varying geometries, usually consisting of right-handed and left-handed mixing baffles disposed in a conduit to perform the continuous division and recombination. Such mixers are generally effective in mixing together most of the mass fluid flow, but these mixers are subject to a streaking phenomenon, which is a tendency to leave streaks of completely unmixed fluid in the extruded mixture. The streaking phenomenon often results from streaks of fluid forming along the interior surfaces of the mixer conduit that pass through the mixer essentially unmixed.
There have been attempts made to maintain adequate mixer length while trying to address the streaking phenomenon. Much of this effort has focused on using a combination of mixing baffles of varying degrees of twist (e.g., using 90° baffles in combination with 180° or 270° baffles). In such designs, the bulk of the mixing is done in the baffles of lesser twist, which reduces the overall length of the mixer. The baffles of greater twist force the fluid from the periphery into the center of the mixing baffles, but such fluid is typically immediately diverted back to the outer periphery. While such approaches do reduce the size of the streaks, the mixing is less efficient because more baffles must be placed in the mixer to thoroughly diffuse these streaks, thus increasing the mixer's length. Such an increase in mixer length can be unacceptable in many motionless mixer applications, such as handheld mixer-dispensers. In addition, longer mixers will generally have a higher retained volume, and higher resulting material waste.
A flow inversion baffle is described in U.S. Pat. No. 6,773,156 to Henning (the Henning '156 patent), the disclosure of which is incorporated by reference herein. The flow inversion baffle produces two flow paths for viscous fluid passing through the mixer. The first flow path redirects fluid from the center of the flow stream to the periphery of the flow stream, while the second flow path redirects fluid from the periphery of the flow stream to the center of the flow stream. It would be desirable to address the streaking phenomenon and further improve the flow inversion baffle.